This invention relates to a photoreceptor used in electrophotography.
In connection with electrophotographic apparatus such as copying machines and document readers, many kinds of materials have been considered for forming a photoconductive layer. Inorganic materials such as Se, CdS and ZnO as well as organic materials such as PVK-TNF have been used previously for this purpose but these previously considered materials generally do not satisfy all the conditions required of a photoreceptor such as properties related to optical sensitivity, spectroscopic sensitivity, signal-to-noise ratio (light resistance/dark resistance), durability and safety to the human body. It has therefore been a common practice to make a compromise to a certain degree regarding certain aspects and make a choice, depending on the individual circumstance under which use is contemplated.
Amorphous silicon, with desirable characteristics such as high optical sensitivity and high durability, has been considered an excellent material. With the conventional photoreceptors of the type having a photoconductive layer of amorphous silicon, however, use is made of a material of amorphous silicon type also for an overcoating layer formed on the surface to protect this photoconductive layer. When ozone is generated by the chargers which are used for charging and erasing, silicon in this overcoating layer reacts with ozone to generate SiO.sub.x on the image forming surface. Since SiO.sub.x has water-absorbing characteristics, electric charges on the surface become diffused easily by absorbed water if humidity is high, causing the image to "run" and thereby adversely affecting the quality of images.